There is a semiconductor device such as a power metal-oxide-semiconductor field-effect transistor (MOSFET) or an insulated gate bipolar transistor (IGBT) in which a gate electrode and a gate insulating film are formed on an inner wall of a trench formed in a front surface of a semiconductor substrate.
A semiconductor device having an MOSFET of a trench structure is disclosed in US 2015/0137177. The semiconductor device includes polysilicon plugs, which contains silicide crystallites and are connected to a source region and a body region of the MOSFET, the silicide crystallites are diffused into a semiconductor substrate by heating, and thus a lifetime killer is introduced to increase a switching speed.